Buttery and chewy, these congo bars seal the deal on everything from a bake sale to a potluck. This recipe, adapted from Cook's Illustrated, is for a 11-by-17 baking sheet for a large batch to serve a crowd, or they freeze well, too.
Preheat the oven to 350 degrees with the rack in the middle position. Spread the nuts on an 11-b-17 rimmed baking sheet and toast until fragrant, about 8 minutes. Transfer to a bowl to cool. Spread the coconut on the baking sheet and toast, stirring 2 to 3 times, until light golden, about 4 to 5 minutes. Transfer to a separate bowl to cool.
Line the baking sheet with foil, overhanging both ends and grease well. Whisk the flour, baking powder and salt in a bowl and set aside.
Whisk the butter and brown sugar together in a mixing bowl. Add the eggs and vanilla and whisk until well blended. Add the flour mixture and stir with a wooden spoon or spatula just until the flour blends in. Fold in the chocolate chips, nuts and coconut and stir to distribute them evenly throughout the dough without overmixing.
Spread the batter evenly into the prepared pan and bake until golden brown and the center springs back, 22-25 minutes. Transfer to a rack to cool completely.
To serve, use the overhanging foil to lift the bars from the pan onto a cutting board. Cut into rectangles, smaller for party-sized servings or larger for a dessert.